Filter support and filter unit construction

ABSTRACT

A filter support with two opposing surfaces having perforations in the central portion and a flat surface surrounding the central portion. The perforations permit passage of fluid between the support surfaces. An inlet and outlet means are attached to the peripheral surface of the holder and the outlet is in fluid communication with the perforations in both support surfaces. A filter unit is formed by sealing a cover and a filter membrane to each flat surface.

- United States Patent [191 Trasen et a1.

FILTER SUPPORT AND FILTER UNIT CONSTRUCTION Inventors: Ben Trasen,Wellesley; Donald B.

Rising, Stow, both of Mass.

Assignee: Millipore Mass.

Filed: Dec. 28, 1970 Appl. No.: 101,850

Corporation, Bedford,

U.S. Cl. ..2l0/455, 210/461, 210/486 Int. Cl. ..B01d 35/02 Field ofSearch ..2 10/321, 455, 74,

References Cited UNITED STATES PATENTS 2/1962 Stecher ..2l0/346 X 51 May1, 1973 3,263,819 8/1966 Schmidt et a1 ..2l0/486 3,522,885 8/1970Lavender et al ..2l0/321 Primary Examiner-Frank A. Spear, Jr.AttorneyClarence S. Lyon, Esq.

[ 5 7 ABSTRACT A filter support with two opposing surfaces havingperforations in the central portion and a flat surface surrounding thecentral portion. The perforations permit passage of fluid between thesupport surfaces. An inlet and outlet means are attached to theperipheral surface of the holder and the outlet is in fluidcommunication with the perforations in both support surfaces. A filterunit is formed by sealing a cover and a filter membrane to each flatsurface.

3 Claims, 8 Drawing Figures FILTER SUPPORT AND FILTER UNlIT CONSTRUCTIONThis invention relates to a filter support and a filter unit utilizingthe filtersupport and filters.

Presently, there are available sealed sterilized filter units comprisinga filter support, a filter and a cover to seal the filter and filtersupport from the atmosphere and to separate the upstream material fromthe downstream material. These filter units are useful only in limitedcircumstances since their capacity is limited by their constructionwherein only one filter surface is available for use. When used, forexample, in intravenous solution preparation, the unit diameter wouldhave to be enlarged to the point where the advantages accruing with unitcompactness would be lost. Thus, there is a present need for a highcapacity, compact, sterilized filter unit.

The present invention provides a novel filter support, a filterconstruction employing the support and a method for making the same. Thefilter support comprises a plate-like structure wherein the two opposingsupport surfaces have a perforated central portion that permits fluidpassage between the two support surfaces. A flat surface surrounds eachperforated central portion. The filter unit is formed by sealing afilter and a cover to each flat portion of the filter support and thecover is spaced apart from the support to permit fluid passage throughthe filter. A conduit extends through the peripheral surface of thesupport and provides means for removing liquid from the interior filtersupport. An inlet means is attached to the peripheral surface of thefilter holder in sealed relationship to permit passage of liquid to eachfilter surface. In use, liquid from the inlet is passed through bothfilters, through both surfaces of the support and through the outletconduit.

The invention will be more fully described with reference to theaccompanying drawings. The drawings show the preferred filtersupportconfiguration wherein each opposing surface comprises a set ofparallel ribs and parallel fluid passages. It is to be understood thatany configuration of perforations in the opposing surfaces of thesupport that permits fluid passage between the surfaces can be used.Thus, one surface can be a set of concentric ribs while the opposingsurface can be a set of radial ribs that are connected to permit fluidpassage to the outlet. Alternatively, the opposing surfaces can comprisea set of circular holes in a flat surface; each set being offset fromthe other so that fluid progresses toward the outlet rather than merelyfilling the holes and remaining static. Each perforation is not so largeas to cause rupturing of the filter membrane during use.

FIG. 1 is a top view of the filter unit of this invention.

FIG. 2 is a side view of the filter unit of FIG. 1, with the inletattachment removed.

FIG. 3 is an isometric view of the inlet attachment.

FIG. 4 is a top view of the filter support.

FIG. 5 is a bottom view of the filter support.

FIG. 6 is a cross sectional view taken along line 6-6 of FIG. 4.

FIG. 7 is a top view of the inside cover surface.

FIG. 8 is an isometric view of a filter support.

Referring to FIGS. 1 and 2, the filter unit generally designated as 1,comprises two covers 2a and 2b, a

filter support 3, a sheet of filter material 4 placed on the one surfaceof the filter support 3 and a sheet of filter material 5 placed on theopposing surface of the filter support 3. The covers 2a and 2b aresealed to the filter support 3 through the filters 4 and 5 to seal theinterior of the filter from the atmosphere and to seal upstream materialfrom downstream material. The seal 6 extends around the entire peripheryof the filter unit 1 where each cover is attached to the filter support.A suitable method for sealing is described in US. Pat. No. 3,471,019and, as described therein, a proper seal 6 will cause the unit 1 andfilters 4 and 5 to appear transparent. The filter unit 1 has an inlet 7and an outlet 8. The inlet 7 is attached to the filter support 3 bybeing placed on fitting 10 which mates with opening 1 1 of the inlet 7.The fitting 10 is shaped so that liquid entering inlet 7 is split todirect one half through inlet 12 in cover 2b and the other half throughinlet 13 in cover 2a. The fitting 10 is not essential to attain thedesired stream splitting. Fluid flow to both filters 4 and 5 is attainedmerely due to the pressure drop through the filters 4 and 5; the fluidbeing directed to the filter having the least pressure drop and to bothwhen the pressure drop is equalized. The liquid in spaces 15 and 16 ismaintained under pressure and is forced through the filters 4 and 5respectively. The liquid enters the spaces in the filter support 3 andexits from the filter unit through conduit 17in the outlet 8.

Referring to FIGS. 4, 5, 6 and 8, the filter support 3 comprises twosets of parallel ribs 20 and 21 which are joined together at theintersections of the respective sets of ribs 20 and 21 so that spacesare formed to permit fluid to pass between the grids 20 and 21. Theouter surfaces 22 and 23 surrounding both sets of ribs are flat toprovide satisfactory sealing of the covers 2a and 2b and the filters 4and 5. The conduit 17 of outlet 8 extends from the interior of thesupport 3 and is in communication with the spaces formed by the grids 20and 21. The hole 25 at the center of the filter support 3 provides ameans for fastening the cover, filters and filter support at the centerthereof thereby providing a stronger filter unit. A smooth portion 26around the periphery of the hole 25 is provided so that the covers canbe sealed to the filter support through the filter in the mannerdescribed above. Alternatively, the central hole can be eliminated.

Referring to FIG. 7, the cover comprises a rim 30 an inside shoulder 31and ribs 32 extending around the periphery thereof. It is also providedwith a hole at the center 33 for passing a rivet therethrough. The coverhas slots 35 and 36 to accommodate the inlet and outlet sections of thefilter support 3. In the slot 35, a relatively small ridge of plastic 37is provided so that excess plastic is melted during the sealingoperation thereby ensuring a perfect seal. This excess plastic is beadedalong lines and 10b on the peripheral surface of the filter unit andprovides ease of attachment of the inlet means 7 thereto. Sufficientexcess plastic is provided in ridge 37 to ensure that after sealing, nosurface crack exists between the fitting 10 and the covers 2a and 2b.The excess plastic preferably is beaded on the peripheral surface of thefilter unit so that the bead is remelted when the inlet means 7 isattached thereto, thereby preventing leakage between the fitting and thecovers and sealing upstream from downstream material. The covers arewelded to the filter holder as for example ultrasonically. The inletconduit 7 then is fitted over the inlet fitting l and is ultrasonicallywelded to the peripheral surface of the filter unit. The inlet is moldedwith a rim of plastic material 40 that provides excess plastic materialmelted during the sealing step and ensures a perfect seal with theperipheral surface of the filter unit.

The filter support is molded as one piece, as for example, in the shapeshown in FIGS. 4, 5 and 6 or 8. In any event, the parallel rib sections20 and 21 are joined at an angle, not necessarily perpendicular, andaround the periphery of the rib section, on both sides of the support, arelatively flat portion is formed. The hole and relatively flat surfacessurrounding the hole at the center of the filter support are optionaland are employed when increased strength of the filter unit is desired.Similarly, the shape of the outlet means need not be as shown in thefigures. However, the conduit associated with the outlet extends intothe interior of the filter support to provide fluid communicationbetween the outlet conduit and the perforations in both surfaces. Inaddition, the main fitting for the inlet means need not be as shown inthe figures. The flat surfaces 22 and 23 are desirable to provide aperfect seal between the cover, filter holder and filters.

Porous membrane filters are made from a material that appearstransparent when there are no holes therein and are placed on bothsurfaces of the filter support 3. Suitable filters are manufactured bythe Millipore Corporation of Bedford, Mass. and sold under the trademarkMillipore and can be formed from a mixture of cellulose nitrate andcellulose acetate having a thickness of about 150 microns. The filtercan have any desirable average pore size, usually ranging from about 0.2to microns.

The parts of the filter unit 1 are assembled as follows:

A membrane filter 4 is placed on a cover 2a inside the rim 30. Thefilter support 3 is placed on the filter and the assembly is weldedtogether. The filter 5 and cover 2b are similarly assembled and weldedto the opposite side of the filter support. Inlet 7 then is assembled infitting 10 and welded in place.

We claim:

1. A filter unit comprising:

a. a dual filter support comprising a plate-like member having twoopposing support surfaces each adapted to support a filter and aperipheral surface connecting said support surfaces, each supportsurface including a perforated portion and an imperforate portionsurrounding said perforated portion, said perforated portions beingdefined by two sets of ribs, one of said sets overlying the other, theouter surfaces of each set of ribs defining the perforated portion ofone of said filter supporting surfaces, the ribs of one set beingnonparallel to the ribs of the other set, and ribs of one set beingjoined to ribs of the other set intermediate said supporting surfaceswhere said ribs cross, adjacent ribs in each set defining fluid flowpassages in the space there-between, and an outlet conduit extendingthrough the peripheral surface of said filter support to permit fluidpassage from at least one of said fluid flow passages to the exterior ofsaid filter support;

a porous filter on each support surface' and a cover means sealed toeach flat surface on said filter support to prevent fluid from bypassingthe filter and peripheral fluid inlet means (for supplying) constructedand arranged to supply fluid to the spaces defined by each of said covermeans and the surface of said filters. 2. The filter unit of claim 1wherein the ribs in each set of ribs are parallel.

, 3. The filter unit of claim 2 wherein the sets of ribs are inperpendicular relationship.

1. A filter unit comprising: a. a dual filter support comprising aplate-like member having two opposing support surfaces each adapted tosupport a filter and a peripheral surface connecting said supportsurfaces, each support surface including a perforated portion and animperforate portion surrounding said perforated portion, said perforatedportions being defined by two sets of ribs, one of said sets overlyingthe other, the outer surfaces of each set of ribs defining theperforated portion of one of said filter supporting surfaces, the ribsof one set being non-parallel to the ribs of the other set, and ribs ofone set being joined to ribs of the other set intermediate saidsupporting surfaces where said ribs cross, adjacent ribs in each setdefining fluid flow passages in the space there-between, and an outletconduit extending through the peripheral surface of said filter supportto permit fluid passage from at least one of said fluid flow passages tothe exterior of said filter support; b. a porous filter on each supportsurface; and c. a cover means sealed to each flat surface on said filtersupport to prevent fluid from bypassing the filter and peripheral fluidinlet means (for supplying) constructed and arranged to supply fluid tothe spaces defined by each of said cover means and the surface of saidfilters.
 2. The filter unit of claim 1 wherein the ribs in each set ofribs are parallel.
 3. The filter unit of claim 2 wherein the sets ofribs are in perpendicular relationship.